The present invention is generally directed to a backup roller assembly for a web-type photoreceptor in an electrostatographic printer. More specifically, the present invention is directed to a backup roller assembly which comprises a thin-walled cylindrical metal tubing filled with a urethane foam. The roller backup assembly of the present invention is useful in a number of imaging processes.
The development of images by various methods, including electrostatographic means, is well known. In several of these methods, toner particles are deposited on an electrostatic latent image present on an insulating surface, such as selenium, utilizing, for example, cascade development, magnetic brush development, powder cloud development, and touchdown development. In view of several disadvantages associated with two-component systems, considerable effort has been directed to designing processes which utilize toner particles only.
In many of the single component development processes, conductive toner particles are selected, and imagewise toner deposition onto the photoconductive member is obtained by induction charging of the toner particles. Electrostatic transfer of conductive toner particles to plain bond paper is, however, usually inefficient as the charge on the toner particles can be reversed by induction charging from the paper during the transfer step. Accordingly, electrophotographic systems wherein conductive single component toner particles are used can require a special overcoated insulating paper to achieve sufficient electrostatic toner transfer. Furthermore, in single component processes with conductive toner particles the control of undesirable background, or background suppression, cannot usually be achieved with electrostatic forces as the toner particles are inductively charged, and deposited on the image bearing member, which is not the situation with two-component developer processes where control of background development is accomplished by electrostatic forces acting on the triboelectrically charged toner particles, causing these particles to be directed away from image bearing members.
In an electrostatographic imaging system using a web-type photoreceptor, the web is entrained by a drive roller around a plurality of backup rollers as it is conveyed past the various stations in the printing process, the backup rollers press from the inside of the web to minimize any undesirable movement of the web. In order for good printing quality to result, the web must be sufficiently taut at the various stations in the printing process so that such undesirable movement does not occur. In addition, it is desirable that the web does not slacken or slip during operation (particularly at the imaging and developing stations), and that the rollers do not damage the web material. It is also desirable that the rollers be lightweight so that the time and power required to start and stop the movement of the web is reduced.
In U.S. Pat. No. 4,221,480 rollers are disclosed which have a plurality of spaced, flexible discs extending outwardly from the exterior surface. The portion or segment of the disc contacting the region of the belt passing thereover provides support therefor. Each of the plurality of discs on the roller supporting the belt are deflected and returned to their original position when not supporting the belt.
U.S. Pat. No. 4,862,211 discloses an apparatus for conveying and rotating an image-forming belt while supporting the belt by at least two rolls. The surface of at least one roll is coated with short fibers such as wool, flax, silk or cotton. The rollers can also be covered with a thread wound around the surface, or a cloth such as made from nylon material.
U.S. Pat. No. 4,910,844 discloses an aluminum roller for conveying a web. The aluminum roller has a surface which is prepared by blasting the surface of the roller with a steel shot to create on the surface a deep texture with well rounded down features and sharp up features with peaks. The blasted surface is finished with a grinding action for removing the peaks to produce plateaus surrounded by interconnected channels. The interconnected channels of the surface allow air entrained between the roller surface and a web to be vented through the channels while the web is in contact with the roller.